Starting-rheostat for electric motors.



No.'690,448. Patented Ian. .7, |902.

F. MACKINTUSH.

STARTING RHEDSTAT FOB ELECTRIC MOTORS.

(Application filed July 15, 1901.)

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m, l Frederick Mackintoah.

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- UNITED STATE-s PATENT OEEICE.l

FREDERICK MACKINTOSI'I, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STARTING-RHEOSTAT FOR ELECTRIC MOTORS.

SPECIFICATION forming part of Letters Patent No. 690,448, dated January 7, 1902.

Application led .l'uly 15, 1901.A

To a/ZZ whont t may concern:

Be it known that I, FREDERICK MACKIN- TOSH, a citizen ofthe United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Starting-Rheostats for Electric Motors, (Case No. 2124,) of which the following is a specication.

This invention relates to devices for controlling electric motors, and can be used with any electrically-driven tool where it is desirable to vary the voltage great-ly and with fine graduations and suppress sparking at the brush or contact conveying1 current to a moving part of the motor.

The in vention is especially valuable in connection with the electric pluggers or mallets used by dentists. The contacts or vibraf tors in these tools are necessarily small and delicate and are quickly burned up if a high voltage is used without some means to prevent the spark when the circuit is broken at each blow of the plugger. Moreover, it is very desirable to be able to regulate the force of the blow through a considerable range.

In the following portion of this specification I shall describe my invention in its use with a dental plugger.

It consists of a rheostat divided into two or more portions connected in series, with means for independently varying one or more of said portions and means for shunting the motor through the variable section of one of said portions. The spark at the motor-contacts is killed by this shunt.

In the accompanying drawings, Figure 1 is a perspective front View of a rheostat embodying my invention. Fig. 2 is a diagram of the circuits. A Y

The several switches and binding-posts are mounted ou the usual slab A, of slate or other insulation, behind which is the customary case B, of perforated metal, to contain the resistance-coils. The line-terminals are connected with the two binding-posts C C and the mallet or plugger terminals with the two binding-posts D D. The posts C and D are A wire 2 leads from the post C to a resistance E, .whose coils are connected with a plurality of contact-points c. A switch-arm F makes contact with any one of Vsaid points, and thereby varies the number of coils in circuit. The switch-arm is connected by a wire 3 with one end of a sec- Serial No. 68,331. (No model.)

ond variable resistance E,preferably through a fixed resistance E2. The coils of the resistance E are connected with a plurality of contact-points e', and a wire 4 connects the other end of said resistance with the bindingpost C'. A switch-arm Gmakes contact with the points e and is connected by wire 5 with the binding-post D. By varying the resistance E the normal voltage supplied to the plugger can be set at any one of several given values. By moving the switch-arm G the voltage can be raised from zero to the limit set by the switch-arm F, the current dividing between the plugger and that portion of the resistance E between the switch-arm Gr and the wire 4, said portion being in shunt to the plugger. There is thus always a closed circuit across the line-terminals, so that the vibrator of the plugger will operate without sparking.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1. In a starting-rheostat, a resistance connected across the line and divided into two or m ore portions one of which is variable, and motor-terminals one of which is connected with one side of the line, and the other with means for connecting it with any point on another portion of said resistance.

2. yIn a starting-rheostat, a resistance connected across the line and divided into two orV more portions, a switch-arm for varying one of said portions, and means for connecting a motor in shunt to a Variable section of another portion.k

'3. In a starting-rheostat, a resistance connected across the line and divided into two or more portions, a switch-arm for varying one of said portions, and motor-terminals one of which is. connected with one side of the line, and the other with a switch-arm making varying contact with another portion of said resistance.

4. In a starting-rheostat, means for varying the total voltage supplied to a motor, and means for varying said voltage and at the same time varying the resistance'of a shunt arou-nd said motor.

In witness whereof I have hereunto set my hand this 13th day of July, 1901.

FREDERICK MACKINTOSI-I.

Witnesses:

BENJAMLN B. HULL, FRED Ross.

IOS 

